Protective and decorative coating compositions such as paints, varnishes, printing inks and enamels contain a film-forming base and other materials such as pigments, extenders, fillers, resins, solvents, thinners, plasticizers, etc. In order to decrease the drying time of such coating compositions, it has been the practice to incorporate therein various drying compositions which have typically been metal salts of organic carboxylic acids such as manganese, lead, cobalt, calcium and iron salts of carboxylic acids such as naphthenic, oleic acid, linoleic acid, octanoic acid, etc. To be useful commercially as a drier, a metal salt should be stable for a long period on storage, and it should be essentially completely soluble in the hydrocarbon solvents or diluents ordinarily used in drier compositions as well as in drying oils. A desirable feature of a drier composition is its ability to effect an even drying throughout the thickness of the film.
In order to provide drier compositions which are capable of affecting more uniform drying of films and coatings, drying compositions comprising mixtures of transition metal salts of carboxylic acids such as cobalt octoate, manganese octoate and various metal perborates such as calcium perborate, have been utilized as curing systems for various coatings including pigmented and unpigmented varnishes including pigmented varnish-ink for lithographic use. The use of mixtures of calcium perborate, manganese octoate and cobalt octoate as a curing system for varnish inks is described in Canadian Patent 1,190,987. The Canadian patent describes methods and compositions for making sheets such as paper sheets or cards covered with superimposed layers of print, the lower of which comprises a "hidden" message which is masked from a reader unless and until an upper coating is removed such as by abrasion, scratching or erasing.